Already among the leaders in abortion restrictions, Missouri could be poised to enact one of the nation's longest mandatory waiting periods for women wanting to terminate a pregnancy.

Missouri legislators are to convene Wednesday for a session devoted to veto overrides, and Republican leaders say they are confident they will overrule Democratic Gov. Jay Nixon's veto of a 72-hour abortion waiting period. The measure contains no exception for cases of rape or incest- an intentional omission that Nixon denounced as "extreme and disrespectful."

The legislation would make Missouri's law the second most stringent behind South Dakota, where its 72-hour wait can sometimes extend even longer because weekends and holidays are not counted. Utah is the only other state with a 72-hour delay, but it grants exceptions for rape, incest and other circumstances.

"Our intent is to make sure that a women has the opportunity to really think through what she's about to do and how it will affect her health, as well as the life of her baby," said Susan Klein, a lobbyist for Missouri Right to Life.

The Missouri legislation is the latest effort in an aggressive, multiyear push by Republican-led legislatures to limit abortions by imposing new requirements on doctors and clinics and mandating that women get a chance to see ultrasounds, listen to heartbeats and view other materials that could cause them to reconsider their decisions.

Some of the measures have been placed on hold by courts, such as a Mississippi law that could force the closure of the state's only abortion clinic by requiring its doctors to have hospital admitting privileges. Similar laws have been at least partly blocked in Texas and Louisiana.

Officials at Planned Parenthood, which operates Missouri's only licensed abortion clinic in St. Louis, have not said whether they would file a legal challenge against a 72-hour abortion waiting period. The clinic's patients travel an average of nearly 100 miles for an abortion, and a three-day delay could force them to either make two trips or spend additional money on hotels, said M'Evie Mead, director of statewide organizing for Planned Parenthood Advocates in Missouri.

Abortion rights groups contend there is no proof that a longer wait will reduce the number of abortions.

"It really is just a cruel way to force a woman to delay her health care," Mead said.

Women also could travel just across the state line in the St. Louis and Kansas City areas to abortion clinics in Illinois and Kansas that don't require as long of a wait.

To override a veto, Missouri lawmakers must achieve a two-thirds vote in each chamber - something that Republicans can accomplish without the need of any Democratic help. When the abortion bill originally passed in May, the House met that mark but the Senate fell a vote short because one Republican was absent. He's expected to be back for the veto override.

The abortion legislation is one of 32 vetoed bills and 136 line-item budget vetoes that Missouri lawmakers will consider overriding. House Speaker Tim Jones ranks it as a priority, along with a vetoed bill expanding tax credits for donations to organizations providing counseling, shelter and aid to pregnant women.

"These are common-sense measures meant to protect life, and we will pass these measures into law over the governor's veto," said Jones.

Missouri has a long history of enacting abortion restrictions that have withstood court challenges. It has required parental consent for minors to get abortions since 1979 and required abortion physicians to obtain surgical privileges at hospitals since 1986. Republican and Democratic lawmakers have twice joined together to override vetoes of abortion bills - enacting what proponents referred to as a partial-birth abortion ban in 1999 and instituting a 24-hour abortion waiting period in 2003.

In less than a decade, three Missouri clinics have quit offering abortions, and number performed in Missouri has declined by one-third to a little over 5,400 last year.